Process of making spark plug electrode structures



Sept. 5, 1961 D. M. YENNI ETAL PROCESS OF MAKING SPARK PLUG ELECTRODESTRUCTURES Filed June 10, 1959 INVENTORS DONALD M. YENNI WALTER A. RUNCKfiwfl ATTORNEY United States Patent 2,998,632 PROCESS OF SPARK :PLUG

E ECTRODE STRUCTURES Donald Ye n dia apoli Ind and W t r Runck, NewYork, N.Y., assignors to Union Carbide Corporation, a corporation of NewYork Filed June 10, 1959, Ser. No. 819,293

3 Claims. (Cl. 29-2512) V This invention relates to spark plugs havingconcentric ring electrodes for internal combustion engines, and moreparticularly to the manufacture thereof.

The invention provides a novel method of making a unitary electrodestructure for spark plugs in which concentric rings of electrodematerial and insulation are formed at the end of such structure by firstspraying onto a suitable base member alternating coating layers ofconductive refractory metal, such as tungsten or molybdenum, andrefractory insulating material, such as aluminum oxide, by means of anelectric arc torch coating process; and then grinding away a portion ofsuch coatings to leave spaced annular electrodes of such conductivemetal on the end of the resulting structure.

A recent modification of spark plug apparatus which has been found to beuseful for automotive engines comprises two ring-shaped electrodesseparated by an annular insulator. Such type of electrode configurationis more resistant to fouling than are the more conventional spark plugelectrodes. It is desired that such electrodes be fabricated from hightemperature metallic materials, but the industry has been plagued withconsiderable failure in satisfactorily forming such electrode apparatus.

The main object of this invention is to provide a method ofmanufacturing spark plug electrode structures, which overcomes suchproblem of the prior art.

In the drawings:

FIG. 1 is a vertical cross section of a suitable base member.

FIG. 2 is a cross section of a 3-layer coating combination applied tosuch base member;

FIG. 3 is a cross section of the finished spark plug electrodecombination of FIGS. 1 and 2;

FIG. 4 is a vertical cross section of an alternate type of suitable basemember having a central passage;

FIG. 5 is a cross section of a finished spark plug using a 3-layercoating combination applied to such base.

A desired electrode configuration can be obtained by using a suitablebase of a type similar to that shown in FIG. 1. This base member ispreferably of metal but could be of ceramic if desired. A coating 11 ofrefractory, electrically conductive metal, especially tungsten, is thenapplied to the end region of the base 10 by means of an electric arctorch plating process. The process using a collimated electric are asdescribed in patent application Serial No. 706,099, filed on December30, 1957, is especially useful in this invention. Additional layers ofrefractory insulating material 12 and refractory electrically conductivemetal 13 are then applied to the coated base member in a similarfashion.

In a final step, the coatings are ground off to the point where adesired exposed surface results and where a controlled annular insulatorlayer 12 is obtained between ring-shaped metal sections 11 and 13. Inoperation, metal ring 13 is then connected to one terminal of the powersupply (not shown) and ring 11 can be connected to the other terminal ofthe power supply through metal base member 10. If the base member 10 isceramic, a wire conductor for ring 11 might be embedded in the ceramicbase member.

' could also contain minor amounts of emissivematerials rice It has beenfound desirable that metal coatings ,11 and 13 have a thickness of about00-10-0020 inch and that the insulator layer 12 be about 0010-0020 inchwide. inch wide. It is understood that the metal coatings such as yttriaor thori'a.

This process is described in more detail in the follow- All are of "2.00amperes and '50 volts was established between a inch dimeter thoriate'dtungsten cathode and a inch diameter water-cooled copper nozzle anodewhile 300 c.f.h. argon passed around the cathode and out through theanode nozzle passage. Tungsten powder (6.8 micron diameter) was passedthrough the nozzle passage at 31 grams per minute and impinged on theend portion of a steel rod of the type shown in FIG. 1 by means of thehigh temperature, high velocity gas efiluent to form a tungsten coatingabout 0.015 inch thick. The coating particles impinged onto the base atan angle of about The tungsten powder flow was then substituted by analumina powder flow of 11 grams per minute to form a 0.015 inch thickcoating of alumina on top of the tugnsten. A third 0.015 inch thickcoating of tungsten was then applied on top of the alumina. The endportion of the resulting coated body was then ground down to level offthe coatings and form the ringshaped tungsten areas separated by analumina layer.

It should be noted that the most successful coating results are attainedwhen the coating apparatus and the body being coated are so positionedthat the coating particles impinge on the desired surface at an angle ofabout 90. Severe angle deviations from this position greatly reduce thequality and bonding strength of the coating.

It is also necessary to apply these coatings in a series of shortcoating intervals of about 3-10 seconds in order to prevent seriousover-heating of the relatively small base structures. In a productionline setup the spark plugs would probably pass through several coatingstations in order to achieve the desired coated body structure.

Electrode configurations obtained in the above manner were tested byconnecting a magneto across the concentric tungsten electrodes. Themagneto was driven by a 1725 rpm. motor, and the sparking action in airwas observed by means of a microscope. This coated spark plug device wasoperated under continuous sparking action for several hours with noapparent wear. Additionaltests of similar electrodes were made in aninternal combustion engine. Simulated operation of thousands of miles ofservice was obtained without noticeable electrode wear.

The specific design of the base material can vary considerably dependingon the desired final spark plug configuration, without departing fromour invention.

As an example of an alternative design, the base member shown in FIG. 4might be used. For purposes of illustration the use of a metal base willbe assumed to aid in cooling the electrodes. Base member 14 could rotatewhile refractory metal coating 16 and insulation layer 17 are applied.The central portion of the coatings would then be trimmed or ground toform an extension of passage 15 in base member 14. An electrical conductor 18 could then be passed through passage 15. Final refractorymetal coating 19 could then be applied to the insulation layer and tothe end of conductor 18 while rotating the base member. The outer edgesof Patented Sept. 5, 1961 The insulator layer is preferably 0010-0015 3the three layers would then be ground to the finished dimension. FIG. 5shows a cross section of the finished electrode structure. Electricalconnection to electrode 16 could be made through an outer conductor (notshown).

What is claimed is: 1. Process of making spark plugs having concentricring electrodes for internal combustion engines, which comprises thesteps of electric arc spraying consecutive layers of refractoryelectrode metal, refractory insulating material and refractory electrodemetal onto the end region of a suitable base member, and grinding awayan end portion of the coatings to provide spaced annular electrodesurfaces on the end region of the base member. 2. Process of makingspark plugs having concentric ring electrodes for internal combustionengines, which comprises the steps of electric arc spraying 0.010-0.020inch thick consecutive layers of refractory electrode coatings oftungsten, alumina and tungsten on the end region of a steel base member,and grinding away an end portion of such coatings to provide on such endregion of the steel base concentric tungsten electrode rings separatedby an insulating alumina ring.

References Cited in the file of this patent UNITED STATES PATENTS Corbinet al. Dec. 9, 1941 Peras Dec. 16, 1958

1. PROCESS OF MAKING SPARK PLUGS HAVING CONCENTRIC RING ELECTRODES FORINTERNAL COMBUSTION ENGINES, WHICH COMPRISES THE STEPS OF ELECTRIC ARCSPRAYING CONSECUTIVE LAYERS OF REFRACTORY ELECTRODE METAL, REFRACTORYINSULATING MATERIAL AND REFRACTORY ELECTRODE METAL ONTO THE END REGIONOF A SUITABLE BASE MEMBER, AND GRINDING AWAY AN